Identification and analysis of the genes responsible for inherited neurodegenerative disorders

现在已知一类新的遗传性人类神经退行性变是由编码多谷氨酸的CAG重复序列扩大引起的。含多聚谷氨酰胺的蛋白质片段在细胞核和细胞质中以聚集形式聚集，并在培养细胞中表达时可诱导细胞死亡，这导致了多谷氨酰胺聚集在发病机制中的重要步骤。支持的是，在患者大脑的神经元和这类神经障碍的转基因小鼠模型的神经元中发现了含有扩展的多谷氨酰胺的核包涵体。我们分析了PC12神经细胞中多谷氨酰胺表达的后果。活化的SEK1聚集在细胞核内，而不是胞浆内的聚谷氨酰胺聚集体中，从而触发细胞死亡。显性负性SEK1(dN-SEK1)可抑制多谷氨酰胺诱导的细胞死亡，但标记有核输出信号的dN-SEK1不能抑制多谷氨酰胺诱导的细胞死亡。稳定状态的Seki表达本身增加了两到三倍。在PML小体中发现的核聚集性聚谷氨酰胺不仅与活化的SEK1共定位，而且还与活化的c-Jun.我们还观察到来自亨廷顿病脑的核包涵体阳性神经元表达SEK1。这项研究提供了多谷氨酰胺病中观察到的神经退变、细胞死亡信号转导激酶级联和与细胞死亡相关的核亚域之间的分子联系。我们认为，含有聚谷氨酰胺聚合体的核PML小体激活了SEK1-JNK激酶级联，导致死亡信号的转导。

A novel class of inherited human neurodegenerations is now known to be caused by expanded CAG repeats encoding polyglutamines. Polyglutamine-containing protein fragments have been shown to accumulate as aggregates in the nucleus and in the cytoplasm, and to induce cell death when expressed in cultured cells, leading to the proposal that polyglutamine aggregation is an important step in the pathogenesis. Supportingly, nuclear inclusions containing expanded polyglutamines have been identified in neurons from patient brains and in neurons from transgenic mouse models of this class of neural disorders.We analyzed the consequence of polyglutamine expression in PC12 neuronal cells. Activated SEK1 accumulated with nuclear but not cytoplasmic polyglutamine aggregations, which consequently triggers cell death. Cell death induced by polyglutamine expression was inhibited by a dominant-negative SEK1(DN-SEK1), but not by DN-SEKI tagged with a nuclear export signal. Steady state SEKI expression itself was enhanced by two to three fold. Nuclearly aggregated polyglutamines, which were identified in PML bodies, colocalized with not only activated SEKl but also activated c-Jun. We also observed that nuclear inclusion-positive neurons from Huntington disease brains expressed SEK 1.This study provides molecular links between neurodegeneration observed in polyglutamine diseases, cell death signalling kinase cascades, and nuclear subdomains related to cell death. We propose that the nuclear PML bodies containing polyglutamine aggregates activate the SEK1-JNK kinase cascade, resulting in transduction of a death signal.